Transparent materials and method of making same



Patented Feb. 22, 1938 UNITED STATES PATENT oFFlcE TRANSPARENT MATERIALS AND METHOD OF MAKIN G SAME No Drawing.

Application June 26, 1934,

Serial No. 732,442

17 Claims.

This invention relates to transparent paper, which is preferably also moistureprooi, and also to a method of producing the same.

Since the advent of widespread use of moistureproof transparent regenerated cellulose sheeting for wrapping foodstuffs, cigarettes, cigars, etc. for the purpose of protecting these variousproducts from dust, air and moisture, while still permitting complete visibility thereof, many attempts have been made to produces. transparent and preferably also moistureproof paper. Most of the investigations have been directed to the production of an improved glassine paper. However; even the improved glassine papers do not possess the glass-clear transparency of regenerated cellulose sheeting. A certain haziness, apparent on wrapped articles, as the dulling of bright colors,

'always exists in the glassine-type paper. Another ency to rupture at sharp folds or at the comers I of packages This is apparent in the film as white spots or lines.

We have found that we can produce a transparent paper by impregnating a highly calendered tissue paper, preferably also containing a wetting agent, with an impregnant, hereinafter more fully explained, which completely fills all the air spaces and voids in the paper. When a moistureproof product is desired, the transparentized paper is coated or impregnated with a moistureproofing lacquer.

It is, therefore, an object of this invention to provide a transparent and preferably also moistureproof paper.

Another object of this invention is to provide a method of producing a transparent and preferably also moistureproof paper.

Other objects will become apparentfrom the following description and appended claims.

The instant invention contemplates impregnating paper with a substantially transparent water-soluble material having an index of refraction substantially the same asthat of the cellulose fibers. When a moisturepro'of product is desired, the impregnated material, after the impregnant has been fixed in any convenient manner, is thereafter coated with a selected moist-ureproofcomposition. The final product is highly transparent, clear, flexible, non-tacky, and possesses good surface slip. It is admirably suited for use as a wrapping tissue.

In the preferred embodiment of the invention, the paper, prior to impregnation, is super-cal endered. Also, in the preferred form of the in-'- vention, there'is incorporated in the paper, prior to the calendering operation, a wetting agent, such as soap, as explained fully in copending application Serial No. 732,440, filed June 26, 1934.

The transparentizing impregnant should completely fill the voids,- spaces, etc. in the paper and fibers thereof. This can be accomplished by any convenient procedure. The paper may, for example, be passed through an aqueous solution containing the impregnant; and the excess solu- 10 tion removed in any well-known manner, such as allowing the excess solution to drain oh the paper or removing the excess by squeeze rolls, doctor knives, metering rolls, etc. The desired amount oi solution containing the impregnant 15 may also be applied by means of transfer rolls, buffers, brushes, etc.- The impregnation with the transparentizing medium may be facilitated by subjecting the paper to vacuurn before, during or after the application of the impregnating solu- .20 tion; by subjecting the papento pressure while it is in contact with the impregnating solution; by the proper maintenance or temperature; or by any suitable combinations of these conditions.

The impregnating material contemplated by 25 the instant invention is of such a nature that it gives the desired extreme flexibility and toughness. The transparentizing impregnants generally are themselves closely related to cellulose in optical properties. Thus, the thoroughly im- 30 pregnated paper amounts to a continuous cellulose film. Due to the nature of the impregnants and the mode of application thereof, bonding be-- tween the celluloseofthe paper and the impregnant is exceedingly strong and softening is 35 age has an undesirable efiect because the solids Q of the solution tend to pull away from the paper fibers during drying, leaving the film in a spotty or hazy condition. Moreover, the shrinkage is sometimes strong enough to actually break thewater-weakened paper.

In so far as the instant invention is concerned, it is to be understood that the impregnating composition may consist of a single compound or a plurality of ingredients dissolved in an appropriate liquid vehicle, such as water, water and alcohol, water and acetone, etc. For example, when an impregnant consists of a plurality of solid ingredients, one component thereof, when used alone, may give highly viscous solution and be of no value for transparency, but when mothfled by the other components may give a composition which gives the desired effect. The preferred impregnating materials are those which are soluble in water to give practically clear solutions and which, when y. give clear films. But, as will be explained hereafter, it is not essential that this be so. The preferred impre nants are also those which, when applied to paper and fixed thereon, leave the paperin a sumcientiy non-tacky state, so that the impregnated film will not stick to itself when wound up.

When the transparent paper is to be given a subsequent coating, such as when the product is to be rendered moistureproof, non-tackiness is of no material importance.

As illustrative examples of the impregnating transparentizing materials contemplated by the instant invention may be mentioned the waterwhlte variety of water-soluble or partly watersoluble substances, such as starch in various stages of deaggregation; thin boiling sizing starches, dextrin; oxidized staches: brewer's body syrups; chlorine-treated starches and other starches hydrolyzed by various means; starch esters and ethers, such as starch acetate to varying degrees of acetylation up to insolubility in alcohol-water or acetone-water mixed solvents; wholly water-soluble gums, including sugar aldehyde, urea-formaldehyde and hydrolyzed vinyl acetate resins; or sugars, such as cane sugar or hydrogenated sugars; sorbitol; various types of degraded or hydrolyzed celluloses, such as hemicellulose or cellulose precipitated from concentrated sulphuric acid solutions or derivatives of various oelluloses which are soluble in water or water-alcohoLsuch as methyl cellulose, glycol cellulose or acetates of degraded cellulose. These materials may be used alone or in combination with each other or in combination with other substances, for example, substances which soften either or both the cellulose and transparentizingimpregnants. As illustrative examples of such softeners may be mentioned glucose, glycerol. glycol or derivatives thereof; soluble oils, such as sulphonated castor oil and hydroxy fatty acids and their salts or These softeners in many cases serve for purposes other than merely flexlbllizing films, for example, they may prevent spottiness of the film; they may increase speed and thoroughness of impregnation; they may increase the transparency of the dry impregnated base. either by elimination of a natural haziness of one of the components of the impregnants or by changing the index of refraction of the composition to more nearly that of the cellulose fibers.

The quantity of transparentizing impregnant incorporated in the paper may vary within wide limits, depending upon the characteristics of the ultimate product. Satisfactory results have been secured when the impreg'nant constitutes approximately 10% to 30%, by weight, of the paper.

The tran'sparentizing impregnant may be incorporated in the paper at practically any stage of the paper-making operation, such as in the beater, on the wire, at the presses, or at any other convenient operation. In the preferred embodiment of this invention, the transparentizing impregnant is applied in an operation subsequent to the manufacture of paper, that is, to a finished paper.

In the preferredembodlment of the invention, the paper base is of the thin, porous type and has the following characteristics:

. Free from opaque filling material.

. Substantially free from water-resisting sizes.

. Has inherently transparent fibers.

. Has a relatively smooth surface, such as may be obtained by super-calendering.

. Is relatively compact, that is, of high solid fraction.

. Of low basis weight, not over about 20 pounds, 24" x 36", 500 sheet ream.

. soap, is incorporated in the paper prior to impregnating, and preferably also prior to supercalendering.

In the foregoing embodiment of the invention, aqueous solutions of the impregnants are contemplated. As an alternative procedure, the instant invention also contemplates passing the paper through a bath of transparentizlng impregnants kept in the fluid state by heat. After passage throughthe molten impregnant and the removal of the excess material from the impregriated paper by any suitable means, the impregnant is solidified in any convenient manner, such as chilling. It is; of course, understood that this procedure is not limited to any precise manner of application, since any procedure and means. will sufjilce as long as there is applied to the paper a. uniform and controllable amount of the molten impregnant. In some cases it is not even necessary to maintain the impregnant in a liquid state until impregnation is complete. Impregnation may proceed even after chilling. This alternative procedure of using molten impregnants possesses the advantage that inexpensive and less complicated equipment can be used. Also, an impregnant that gives the paper a relatively tacky surface can be used without. very great trouble, since the impregnated paper may be surfaced, without the tacky paper ever coming into contact with any supporting mechanism, with a non-tacky coating.

As illustrative examples of substances which can be used in the molten condition may be mentioned glucose, sugar, sorbltol, sugar aldehyde resin, acetone formaldehyde resin, or any other material having similar melting and solvent properties. It is desirable that the materials melt at a temperature below the charring point thereof and be relatively fluid at temperatures below'the point where the paper is harmed or appreciably embrittled. This temperature for the most part is below 120 C. When the abovementioned materials melt at too high temperatures or melt to form liquids too viscous for good impregnation, a small quantity of water may be added thereto. The amormt of water added is preferably limited to such an amount that the swelling of the paper is slight. Also, the quantity of added water is suchthat it can be evaporated while the film is yet unsupported and still produce anon-wrinkled and non-distorted film. To accomplish the removal of this small amount of added water, which is preferably reduced only to an extent at which it is in. equilibrium in the impregnated paper with room conditions of temperature and humidity, there is provided a short drying chamber maintained at an elevated temperature through which the film is passed after leaving the impregnating bath and the surplusremoving devices.

In this alternative procedure, paper of the more porous type, such as super-calendered tissue, is preferred, because these papers are subject to the most complete impregnation in the shortest time.

The transparentizing impregnants hereinbefore mentioned have many advantages. Once the paper has been transparentized therewith, it may be moistureproofed by practically any known process without any detrimental elfects or serious complications. The water-soluble impregnants are of such a nature that they are not substantially disturbed or altered by practically any known method 01' moistureproofing Thus, the instant process, in contradistinction to other processes, does not limit the composition and methods which may be used for the application of a subsequent coating.

When the transparent paper hereinbefore described is to be moistureproofed, any suitable moistureproofing composition may be appliedthereto. As illustrative moistureproofing compositions'may be mentioned those which consist of the following ingredients in such proportlons as to give thin, transparent, moistureproof, non-tacky coatings:

1. Cellulose derivative, wax, and solvent:

2. Cellulose derivative, wax, plasticizer, and

solvent;

3. Cellulose derivative, wax, gum, and solvent;

4. Cellulose derivative, wax, gum, plasticizer,

and solvent;

5. Resin, wax, and solvent;

6. Resin, wax, plasticizer, and solvent;

7. Wax compositions.

. Though the invention has been described in connection with the production of transparent paper, that is, plain glass-like films, the process may be modified to obtain various results, such as colored products. Colored films may be produced by dyeing the paper, by dissolving a dye in the impregnating solution or in the moistureproofing composition, or a coloring substance may be applied at any convenient stage in the preparation of. the transparent paper. The paper may be dyed one color and the impregnants dyed another color, whereby mottled effects are secured. The paper may be embossed or designs pressed 'thereinto. Additional crystallizing materials may be incorporated in the impregnant toyield frosted designs.

ljor the purposes of this specification and claims, we, define moistureproof materials as those which, in the form of continuous, unbroken sheets or films, permit the passage of not more than 690 grams of water vapor per 100 square 5 meters per hour, over a period of 24 hours, at

approximately 39.5" C.0.5 C., the" relative hu-- being maintained at least at 98% and the relative humidity of the atmosphere at the other side being maintained at such a value as to give a humidity differential of at least Moistureproofing coating compositions are defined as those which, when laid down in the form of a thin, continuous, unbroken film applied uniformly as a coating with a total coating thickness not exceeding 0.0005" to both sides of a sheet of regenerated cellulose of thickness approximately 0.0009", will produce a coated product which is moistureproof. For the purposes 'of experimental tests, especially for those materials adaptable as coating compositions, moistureproof materials include those substances, compounds or compositions which, when laid down in the form of a continuous, unbroken film applied uniformly as a coating with a total coating thickness not exceeding 0.0005" to both sides of a sheet of regenerated cellulose of thickness approximately 0.0009", will produce a coated sheet which will permit the passage therethrough of not more than 690 grams of water vapor per 100 square meters per hour over a period of approximately 24' hours, at a temperature of 395 C.:0.5 C. (preferably 39.5? C.- -0.25 C.), with a water vapor pressure differential of 50-55 mm. (preferably 53.4103! mm.) of mercury. For convenience, the number of grams of water vapor passed under these condi-.

uncoated regenerated cellulose sheet.

In order to more fully explain the nature of the instant invention, the following illustrative examples are set forth:

Example I (A) A thin porous sulphite tissue between 13 pounds and 18 pounds basis weight (24 x 36-500) is treated 'with'the following solution consisting of the ingredients in approximately the proportions set forth:

- I Per cent by weight Ammonium oleate 1.9

Water 4 21.0 Denatured alcohol 77.1

The excess soap solution is'removed by means of squeeze rolls and the wet tissue is passed over dryer rolls. The drying is continued until the tissue feels distinctly moist (10% to 15% moisture). The damp tissue is passed through a supercalender stack, the rolls of which are cooled. This is followed by a second super-calendaring operation in which heated rolls are used. If desired, these calendaring operations may be combined, as by using a stack in which one-half the rolls are cooled, the other heated. As the tissue emerges from the hot calender rolls, it is dry and has a fine finish. While its solid fraction has been consideriatbly increased, the calendered paper still retains a good proportion of its ab- .sorptiveness.

An uncoated sheet of regenerated cellu- The starch acetate is prepared by refluxing corn starch with equal parts of glacial acetic acid and acetic anhydride for 1 hour. The starch, acetylated to about 12% acetyl content, is illtered, washed free of acid with methanol, and dried. The dried product is used inthe above composition. Small amounts of acid catalysts, such as sulphonic acids, may be added in the starch acetate preparation to facilitate acetylation and to reduce the viscosity of the product.

In preparing the above composition, the starch acetate is first dissolved by making a smooth paste of the starch acetate with equal parts of water, then adding the remainder of the water and glycerol and heating the whole solution nearly to boiling. The solution prepared will be slightly viscous and very slightly milky.

The impregnating solution is applied to the paper by immersing the paper into the solution held at 20 C. to 70 C. The excess is immediately removed by passing the paper between squeeze mils or through scraper rods. Sum- .cient solution is left on the paper so that when the water is evaporated about 20 pounds to 30 pounds of impregnant to 100 pounds of paper remain. After removing the excess solution, the paper is carried over cold rolls for a sufl'icient period of time to allow thorough impregnation. This time is usually about 5 seconds to 10 seconds. The paperis then passed over hot rolls to evaporate the water, and the dried film is wound up.

The paper thus produced is transparent, free from any white haze or spottiness, glossy, nontacky, and. when in equilibrium with room humidity, of exceptional flexibility and toughness.

(B) The transparent flexible product of Example HA) is coated with a moistureprooflng lacquer consisting of the following compomtion:

Solids Nitrocellulose Gum dammar 34 'Iricres'yl phosphate i2 Solids conten 15 The transparent film is passed through the above lacquer, held at C. to 45 C. and then passed through knives which remove all but a thin uniform layer of lacquer. The filmis then passed into a chamber held at 60 C. to 100 C. for such a time as is necessary to evaporate the lacquer solvents. 1!. any considerable amount of moisture is lost from the base him during the Paraiiin wax--- Per cent by weight drying operation, the coated paper is conducted through a humidifying chamber maintained at 40 C. to 70 C. and 60% to relative humidity to restore the film to its normal moisture content, and the fllm wound up.

The product obtained is moistureprooi, transparent, non-smeary', non-tacky, glossy and free from spots or white haze. Furthermore, its flexibility and toughness is such that it can be creased and folded without the appearance of white lines.

(C) The transparent, flexible film obtained in Example HA) is passed through a melt of the following composition:

Per centbyweight White parafnn wax 47 Refined carnauba wax 47 Rubber (crepe) 8 The paper is passed through the molten composition and then through a set of two doctor knives on each side of the film by which all but a uniform layer of composition is scraped from the film. About 5 pounds of the wax composition to 100 pounds of the transparent film are applied.

The product obtained is moistureproof, transparent, glos y, free from white haze, non-smeary, and sufliciently tough and flexible to withstand drastic flexing and creasing without showing undesirable white lines.

Example 11 (A) The same calendered paper as in Example 1(A) is impregnated and dried exactly as in that example, but using the following impregnating solution:

'Ihe fllm obtained is glossy, non-tacky, free from white spots or haze, and of exceptional flexibility. Its transparency is somewhat better than that oi-Example I(A) since the refractive index of the impreanant is more nearly that of the cellulose.

(B) A moistureproof, transparent, and flexible film is produced from the product of Example IHA) by coating it with the following composition and by the procedure outlined in lixample 1(3) Per cent by weight Pyroxylin 5.21' Gum dammar 3.22 Dibutyl phthalate 2.30 Paraflln (62 C. M. P.) 0.88 Zinc steam 0.11 'I'oludl 35.63 Ethyl acetate 45.76 Ethyl alcohol 6.22 Acetone 0.67

A product is obtained which is equal to that a (C) The same calendered paper as in Example I(A) is treated with the following impregnating solution:

Per cent by weight Starch acetate (high acetyl content) 20 Sorbitol; 10. Water 30 Denatured alcohol--. 40

The paper is passed through the impregnating solution and then through squeeze rolls to remove the excess solution. When impregnation is complete, the paper is passed over hot dryer rolls and the paper dried.

There are some advantages in using the higher starch acetate. The above solution is usually somewhat less viscous than previous starch acetate solutions and, therefore, it more v rapidly penetrates or impregnates the paper; the starch acetate of higher acetyl content usually results in a more transparent film; the use of alcohol in the impregnating solution decreases the softening power which water has on the thin tissue, so that there is less likelihood of breakage in the impregnating solution.

The product obtained is very transparent and glossy and of excellent flexibility. It may be moistureproofed with any convenient composition and means.

Example III (A) The same paper as in Example HA) is given the same treatment as in Example 1(A) except that the following impregnating solution is used:

i Per cent-by weight Sizing starch 20 40 Glucose 20 Water 60 The sizing starch used here is a hydrolyzed corn starch commercially produced by the Corn Products Refining Company and sold as Amidex the film in this condition after drying, it ispassed directly into a moistureprooflng lacquer and coated as in Example 103). Y

The moistureproof product obtained will possess its original flexibility and toughness and in addition will have imparted to it by the coating procedurea good degree of transparency and gloss, and will be free from any haziness or spottiness.

(B) A transparent, flexible film, similar to that obtained in Example II(A), except for a slightly greater degree of tackiness, is obtained if the calendered sulphite tissue, instead of being impregnated with a starch acetate solution, is impregnated with a solution of the following composition:

Per cent by weight Oxidized starch 20.0 Sorbitol 7.5 Glycerol.. I 2.5 Water 70.0

Somewhat highly oxidized starch, such as a thin British gum, may be used. The product obtained, while being transparent and flexible, is too tacky to betwound up on itself. Consequently, it is desirable to apply immediately any suitable moistureprooflng composition by which atransparent and flexible film is obtained and through which tackiness is eliminated.

Example IV (A) A tissue between 13 pounds and 18 pounds basis weight (24 x 36-500) is passed through a calender, preferably in a slightly moistened condition.

The calendered paper is impregnated with a 50% sorbitol solution in water by supplying about 10 pounds of solution to 100 pounds of paper to each side of the film with suitable hoppers. The paper ispassed over cold rolls until impregnation is complete, and-then over hot rolls to expel the water. Without winding the film up, it is immediately coated with a moistureproofing lacquer following the procedure in Example 103). The product obtained will be moistureproof, free from "haze or spots, transparent and very flexible.

(B) A good grade of glassine, 20 pounds basis weight, is passed through a 50% sorbitol water solution and then through squeeze rolls to remove all but about 15 pounds to 30 pounds of solution, to 100 pounds of glassine. The paper is rolled up and allowed to stand for l to 5 hours. During the time of standing, a limited amount of swelling proceeds (the full swelling power of the water is limited by. the high concentration of sorbitol) and the sorbitol slowly penetrates into the film. displacing the entrapped air.v When the glassine has been sufilciently impregnated, it is dried on dryer rolls or other suitable means, and the tacky transparent film passed through a moistureproofing lacquer as Per cent by weight Resin 3o Glycerol 5 Water 65 The resin used in this example is the condensation product of acetone and formaldehyde, a slightly yellow, slightly brittle resin. The resin solution is applied, the water evaporated, and the product coated with a lacquer as in Example IV(A). A glossy, non-smeary, moistureprooi' product of high transparency and great flexibility is obtained.

1Emample V (A) The same calendered tissue as in Example I(A)- is impregnated as follows: The paper is WM through a tank containing sorbitol'which has been heated sumciently to be a slightly vis- 'cous liquid, then out of the tank and through doctor knives so adjusted as to remove all but about 10 pounds of sorbitol for 100 pounds paper. It is preferable that the surface of the paper be completely covered with a thin -fllm of the sorbitol. The sorbitol is kept in a molten condition until the paper is thoroughly impregnated and is then cooled by a blast of cold air or is simply allowed to cool oi. itself. The impregnated paper is passed between suitable hopper lips or over transfer rolls by which a molten wax composition similar to that of Example 1(D) is uniformly applied to both sorbitol sur!aces. If the original sorbitol bath contains the proper amount 01' moisture, it is not necessary to further humidity the film.

The product obtained is very glossy and transparent, moistureprooi, non-tacky and nonsmeary, and of exceptional flexibility.

(B) The same paper is given the same treatment as in Example IV(A) except that a molten bath of the following composition is substituted for the sorbitol:

Percent by weight Glucose 70 Corn syrup- 30 With this composition it is not necessary to allow impregnation to proceed fully to completion before chilling the molten composition, since impregnation with this composition proceeds slowly, even at room temperature. The product will be similar in all respects to that of Example V(A) (C) The same paper as in Example I(A) is impregnated with:

The paper is passed through this solution held at a sufilciently high temperature to be fluid, thence out of the solution and through suitable doctor knives or squeeze rolls to remove the excess. Aiter removal of the excess solution, the film is'passed through a short drying chamber held at an elevated temperature, by which the water is evaporated to such a content as to bein equilibrium with room humidity. The impregnated paper is then passed through a moistureprooflng lacquer and coated by the same procedure as outli ed in Example 1(B) The prod t obtained is non-tacky, nonsmeary, glossy and of very good transparency and flexibility.

Though the invention has been particularly described in connection with transparent and moistureproof paper, the principles thereof are equally applicable to non-moistureprooi', such as, for example, waterproof, and transparent paper.

Since it is obvious that various changes and modifications may be made in the above description without departing from the nature or spirit thereof, this invention is not restricted thereto except as set forth in the appended claims.

We claim:

l. A transparent moistureprooi' material comprising paper containing a wetting agent and having its voids and spaces substantially completely filled with a water-soluble impr gnant and thinly coated with a transparent moistureproofing composition, said impregnant being present in an amount of 10% to 30%, by weight,

T of the paper.

2. "A transparent moistureprooi material comprising highly calendered porous paper containing a wetting agent and having its voids and spaces substantially completely filled with a water-soluble impregnant and thinly coated with a transparent moistureprocilng composition, said impregnant being present in an amount of 10% to 30%, by weight, of the paper.

' 3. A method of making a transparent material which comprises incorporating a non-volatile wetting agent in paper, highly calendaring the paper, impregnating said paper to substantially completely fill the spaces and voids thereinwith a water-soluble transparentizing agent whereby the paper is transparentized, and finally applying a transparent, moistureproof coating to the transparentized paper.

4. A method of making a transparent material which comprises incorporating a non-volatile wetting agent in paper, highly calendering the paper, impregnating said paper to substantially completely fill the spaces and voids therein with an aqueous solution containing a water-soluble transparentizing agent, evaporating the water whereby the paper is transparentized, and finally applying a transparent, moistureprooi' coating to said transparentized paper.

5. A method of preparing transparent material which comprises incorporating a non-volatile wetting agent in paper, highly calendering the paper, impregnating said paper to substantially completely fill the spaces and voids therein with a water-soluble transparentizing agent in the molten state, setting the impregnant whereby the paper is transparentized, and finally applying a transparent, moistureproof coating to the transparentized base.

6. A method of making a transparent material which comprises incorporating a non-volatile wetting agent in paper, highly calendering the paper, impregnating said paper to substantially completely fill the spaces and voids therein with a water-soluble substance selected from the class which consists of starches and starch compounds; and hydrolyzed vinyl resins; whereby the paper is transparentized, and applying a transparent moistureprooilng coating.

7. A transparent material comprising highly calendered paper containing a wetting agent and having its voids and spaces substantially completely filled with a water-soluble substance selected from the class which consists of starch and starch compounds, said substance being present in an amount of 10% to 30% by weight of the paper, said paper being thinly coated with a transparent moistureprooi composition.

8. A transparent moistureproofing material comprising paper containing a wetting agent distributed throughout its mass and having its spaces and voids substantially completely filled with a transparentizing water-soluble substance, whereby said paper is transparentized.

9. A transparent moistureproofing material comprising paper containing a wetting agent distributed throughout its mass and having its spaces and voids substantially completely filled with a transparentizing water-soluble substance whereby said paper is transparentized, said paper being thinly coated with a transparent moistureproofing composition.

10. A transparent material comprising highly calendered paper containing a wettin g agent distributed throughout its mass/and having its spaces and voids substantially completely filled with a water-soluble substance selected from the class which consists of starch and starch compounds;

11. A transparent material comprising highly calendered paper containing a wetting agent distributedthroughout its mass and having its spaces and voids substantially completely filled with starch acetate.

/ 12. A transparent material comprising highly calendered paper containing a wetting agent distributed throughout its mass and having its spaces and voids substantially completely filled calenderecl paper containing a wetting agent distributed throughout its mass and having its spaces and voids substantially'completely filled with a water-soluble substance selected from the class which consists of starch and starch compounds, said paper being thinly coated on each side thereof with a transparent moistureproof composition.

15. A transparent material comprising highly calendered paper containing a wetting agent distributed throughout its mass and having its spaces and voids substantially completely filled with starch acetate, said paper being thinly coated on each side thereof with a transparent moistureprooi. composition.

16. A transparent material comprising highly calendered paper containing a wetting agent distributed throughout its mass and having its spaces and voids substantially completely filled with chlorine-treated starch, said paper being thinly coated on each side thereof with a transparent moistureproof composition.

17. A transparent material comprising highly calendered paper containing a wetting agent distributed throughout its mass and having its spaces and voids substantially completely filled with oxidized starch, said paper being thinly coated on each side thereof with a transparent moistureproof composition.

' DONALD E. DREW.

- THERON a. FINZEL. 2a 

